1. Field of the Invention
The present invention relates to an exposure mask substrate manufacturing method, an exposure mask manufacturing method, and a semiconductor device manufacturing method.
2. Description of the Related Art
In recent years, problems in photolithography in the semiconductor manufacturing process have become noticeable. Along with the progress in size reduction of semiconductor devices, the need for micropatterning in photolithography has grown. The device design rule has already been reduced to 0.1 μm, and the pattern size to be controlled is 10 nm or less. That is, the accuracy required is very strict.
Under these circumstances, the problem of flatness of photomasks used in photolithography has risen as a factor that impedes highy accurate pattern formation. As the focus margin in photolithography decreases along with size reduction of devices, the flatness of a photomask has become non-negligible.
When the shape of a photomask chucked in an exposure apparatus is predicted by simulation, the flatness of the photomask can be managed in actual use. Hence, the number of problems caused by the flatness of photomasks is becoming smaller than before where the flatness is not predicted.
However, there is still a problem that a photomask shape predicted by simulation does not coincide with the shape of a photomask actually chucked in an exposure apparatus. This is because a light-shielding film formed on the photomask has internal stress. In a photomask having a pattern with a large opening ratio, stress relief caused by removing the light-shielding film by etching changes the flatness of the mask.